As is known, many pourable food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized sheet packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
In particular, the packaging material has a multilayer structure comprising a base layer for stiffness and strength, which may include a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material, and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; in particular, the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled continuously downwards with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then fed to a folding unit to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
In both the above cases, given numbers of finished packages have to be grouped and packed in packing materials, e.g. cardboard and/or plastic film, to form modules for transport to retailers, also commonly known as “multi-packs”.
For this purpose, the packages exiting from the folding unit have to be sequenced and grouped to form a plurality of package batches, which are formed by given numbers of packages and are designed to be combined together to form the multi-packs; in particular, the batches arrive at the station for the creation of the multi-packs arranged at the desired distances from one another; then, such batches are picked up by a manipulator to be combined with other batches to form the multi-packs.
Conveyor systems based on linear motor technology have been recently proposed for sequencing and grouping items, in particular packages or containers. These conveyor systems basically comprise a closed loop track, which houses a stator armature formed by a plurality of individually-excitable solenoids, and a plurality of movable elements or carts, which house respective permanent magnets and are independently moved along the track by individually controlling the solenoids. By loading the packages onto respective carts, it is possible to drive them in the desired way along the track, such as grouping a given number of packages to form a package batch and also defining a given distance between each group of carts carrying the packages forming one package batch and the carts forming the previous and following package batches.
This technology is extremely flexible as it permits to group any number of packages without carrying out any structural change to the conveyor system but simply varying the position/speed/acceleration profile imposed to each cart and enables high capacity solutions (high numbers of packages per hour).
However, the proposed solutions have the following drawbacks.
First of all, the packages have to be transferred from the traditional conveyor, by which they are advanced when they exit from the folding unit, to the individual carts. This operation requires to provide an additional conveying module interposed between the traditional conveyor and the linear motor conveyor system and which permits to load the packages on the carts without damaging them. This means to increase complexity and costs of the packaging lines.
Moreover, the carts have to be structured and designed to support the entire weight of the packages when they travel along the track; this entails high traction forces to drive the packages to the station for the creation of the multi-packs.